Pyrometallurgical processes for recovering metals such as lead from ore deposits are well-known in the art and used extensively throughout the industry. However, since the lead in such ores exists primarily in combination with sulfur or sulfur-bearing materials, pyrometallurgy leads to the oxidation of these sulfur materials and the formation of sulfur oxides.
Air pollution regulations and standards, promulgated by both federal and state agencies in recent years, have placed severe restrictions on permissible sulfur oxide emission levels from such processes. While the industry has developed numerous methods for recovering sulfur oxides emitted from pyrometallurgical processes, such techniques are highly expensive. Indeed, the anticipated advent of yet more stringent pollution standards may impose technologically impossible, as well as economically unfeasible, demands on the industry.
Hydrometallurgical techniques for recovering metals, however, offer an attractive alternative emission control approach since they do not result in the formation of sulfur oxides. Rather, hydrometallurgy permits the recover of sulfur in its elemental form. Despite this seemingly simple solution to the emission problem, however, hydrometallurgy is economically competitive with pyrometallurgical processing only if near complete recovery of the desired metal from the ore is effected, a condition difficult to achieve on a commercial scale utilizing current hydrometallurgical techniques. To offset these costs it is further desired to effect complete recovery of all other metals present within the ore.
The foregoing problems are particularly pronounced where the desired metal exists in a low grade deposit since the costs per unit of metal produced are extremely high. In particular, low-grade lead concentrates containing copper, zinc and silver cannot be economically processed unless a near complete recovery of all these metals is obtained. Heretofore, hydrometallurgy has not been successful in selectively recovering the variety of metals contained in such concentrates.
It is accordingly an object of this invention to selectively recover, in high yields, a number of valuable metals from ores containing such metals.
A further object of this invention is to accomplish the foregoing recovery utilizing hydrometallurgical techniques.
A more specific object of this invention is to selectively recover lead, copper, zinc and silver from low grade concentrates containing such metals.
These and other objects will become more apparent upon reading the more detailed description which follows.